Electronic component mounting apparatus and electronic component mounting method

ABSTRACT

In the electronic component mounting apparatus, a vertical load and horizontal loads applied to an electronic component are detected by a load sensor that have piezoelectric elements provided in a stack in the mounting direction of the electronic component. Therefore, the size in the horizontal direction of the load sensor can be reduced, and the load applied to the electronic component can be detected at the neighborhood of the mounting position of the electronic component. Moreover, by comparing a position in a two-dimensional space in which the load values in the X-direction and the Y-direction of the horizontal load are served as coordinate values with a tolerance range in the two-dimensional space, mounting failure can be detected from a deviation in the horizontal loads.

BACKGROUND OF THE INVENTION

The present invention relates to an electronic component mounting apparatus and electronic component mounting method for mounting electronic components of, for example, semiconductor bare chips, electronic circuit packages and the like on a board.

Conventionally, in mounting an electronic component such as a semiconductor bare chip with bumps on a board, there has been adopted a method for bonding the bumps to electrodes on the board by applying a load to the electronic component against the electrodes. According to this method, it is required to control the value of the load applied to each bump within a prescribed range, and therefore, mounting of the electronic component has been carried out while measuring the load applied to the electronic component by means of a load sensor such as a load cell.

FIG. 12 shows the construction of a conventional electronic component mounting apparatus. In the conventional electronic component mounting apparatus 100, a movement block that moves in a Z-direction is divided into a first movement block 110 and a second movement block 120, and a nut section 121 provided in the second movement block 120 is meshed with a feed screw 151 that is rotationally driven by a motor 150. Moreover, the first movement block 110 and the second movement block 120 are joined so as to be pulled together by a spring 122, and a load cell 130, which is a load sensor, is provided between the first movement block 110 and the second movement block 120. A slider 111 is provided on a side surface of the first movement block 110 and slides on a guide rail 112 provided in the Z-direction.

The lower end portion of the first movement block 110 is provided with a shaft 113 whose central axis is arranged in the Z-direction and a holding head 115 for sucking and holding an electronic component 101 by a negative pressure, in this order. Moreover, a table 140 movable in an X-direction and a Y-direction is provided below the holding head 115, and a board 102 is placed on the table 140. An output of the load cell 130 is inputted to a control section 160, and the control section 160 controls the driving of the motor 150 while monitoring the output of the load cell 130.

When mounting the electronic component 101 on the board 102, the motor 150 is rotationally driven in a prescribed direction to move down the second movement block 120 and the first movement block 110 in the Z-direction. When the electronic component 101 is brought in contact with the board 102, the load detected by the load cell 130 gradually increases, and the electronic component 101 is pressurized. At this time, by applying, for example, ultrasonic waves while pressurizing the electronic component 101 with a prescribed load, bumps 101 a provided at the bottom of the electronic component 101 are connected to the wiring pattern on the board 102 and then mounted. Subsequently, the holding head 115 is separated from the electronic component 101, and the second movement block 120 and the first movement block 110 are moved up in the Z-direction.

As a prior art relevant to the conventional electronic component mounting apparatus, Japanese unexamined patent publication No. 10-163273 discloses an electronic component mounting apparatus in which the first movement block and the second movement block are joined together via an air cylinder instead of joining the first movement block and the second movement block together by means of a spring. Japanese unexamined patent publication No. 08-203966 discloses an electronic component mounting apparatus in which a voicecoil motor is employed in place of the motor and screw feed mechanism in order to move the movement block in the Z-direction, and the holding head is attached to a shaft driven in the Z-direction by the voicecoil motor. Further, in Japanese unexamined patent publication No. 08-203966, a pressurizing force is estimated from a current applied to the voicecoil motor using no load sensor like the load cell.

Japanese unexamined patent publication No. 11-297764 discloses an electronic component mounting apparatus in which the electronic component and the board surface are made parallel to each other by detecting a pressure during bonding by means of load sensors provided in a plurality of places on the holding head side and adjusting the inclination of the lower surface of the holding head so that the value of the pressure becomes uniform.

Japanese unexamined patent publication No. 04-94553 discloses an electronic component mounting apparatus in which, in a bonding device for carrying out bonding by pressurizing a tape board against an electronic component placed on a table with the bumps directed upward, the inclination of the table is adjusted so that the pressurizing surface of the bonding tool and the bonding surface of the electronic component become parallel to each other on the basis of pressurizing forces detected by strain gauges provided in a plurality of places of the bonding tool that holds the tape board. Japanese unexamined patent publication No. 04-223349 discloses an electronic component mounting apparatus in which the inclination of a stage is adjusted on the basis of outputs of load sensors provided in a plurality of places of a table. Further, Japanese unexamined patent publication No. 04-223349 discloses a technique for making the pressurizing force of the bonding tool coincide with the pressurizing pattern by carrying out feedback control on the basis of an output of another load sensor provided for the bonding tool.

In the conventional electronic component mounting apparatus 100 shown in FIG. 12, the load cell 130 is positioned between the first movement block 110 and the second movement block 120, and the slider 111 and the guide rail 112 are provided on the (−Z) side (lower side) of the load cell 130. The generation of some degree of sliding resistance (e.g., about 30 gf) cannot be avoided when the slider 111 slides on the guide rail 112, and the load detected by the load cell 130 includes an error due to this sliding resistance. Therefore, if the driving of the motor 150 is controlled on the basis of the load detected by the load cell 130, then there occur variations in the load applied to the electronic component 101. If the load actually applied to the electronic component 101 is extremely smaller than the required load, then a sufficient strength for the bonding between the electronic component 101 and the board 102 cannot be obtained, possibly causing contact failure or the like. Conversely, if the load actually applied to the electronic component 101 is extremely larger than the required load, there is the possibility of the occurrence of collapse of the bumps 101 a at the bottom of the electronic component 101 or the damage of the electronic component 101 itself.

Moreover, since only the load in the Z-direction is detected by the load cell 130 in the electronic component mounting apparatus 100, if the electronic component 101 is inclined with respect to the surface of the board 102, then the load is not uniformly applied to the bumps 101 a at the bottom of the electronic component 101, possibly causing the contact failure of some bumps and the collapse of some bumps. Such an issue occurs similarly in the electronic component mounting apparatus of Japanese unexamined patent publication No. 10-163273. Moreover, the load applied to the electronic component is detected only in the Z-direction also in the electronic component mounting apparatus of Japanese unexamined patent publication No. 08-203966, and the measurement is carried out indirectly. Accordingly, there are the possibilities of the contact failure between the electronic component and the board, the collapse of bumps and the damage of the electronic component itself.

In the electronic component mounting apparatuses of Japanese unexamined patent publication Nos. 11-297764, 04-94553 and 04-223349, it is possible to detect the inclination of the electronic component and the board by means of a plurality of load sensors arranged in the horizontal detection. However, it is required to separately provide the load sensors in a plurality of places of the apparatus in order to appropriately measure the load. Conversely, if the load sensors are separated from the mounting position, regions occupied by the load sensors are disadvantageously increased. That is, according to the technique of arranging the plurality of load sensors in the horizontal direction, there is a limit to the accuracy of the sensor sections in detecting the inclination of the electronic component with respect to the board surface, and it becomes difficult to accurately detect the mounting failure.

Moreover, in order to remove the above issue that when the electronic component 101 is inclined with respect to the surface of the board 102, the load is not uniformly applied to the bumps 101 a at the bottom of the electronic component 101, possibly causing the contact failure of some bumps and the collapse of some bumps, it is possible to use, for example, an air bearing in order to reduce the sliding resistance when the movement block is moved in the Z-direction. However, although the load can be supported by the air bearing when the load applied to the electronic component is small (e.g., about 300 gf), the air bearing cannot be used when a load that exceeds a prescribed limit is applied. Such the issue occurs similarly in the electronic component mounting apparatus of Japanese unexamined patent publication No. 10-163273.

In the electronic component mounting apparatus of Japanese unexamined patent publication No. 08-203966, the holding head is moved while being attached to the shaft driven in the Z-direction by the voicecoil motor, and therefore, a sliding resistance is generated similarly to the case of FIG. 12. Moreover, since the load applied to the electronic component is indirectly measured, there are the possibilities of the occurrence of the contact failure between the electronic component and the board, the collapse of the bumps and the damage of the electronic component itself, as described above.

Likewise, in the electronic component mounting apparatuses of Japanese unexamined patent publication Nos. 11-297764, 04-94553 and 04-223349, the load applied-to the electronic component is indirectly measured by an inclination adjustment mechanism or the like, and therefore, it is difficult to accurately measure the load actually applied to the electronic component. Therefore, it is difficult to accurately carry out the adjustment of the inclination of the electronic component with respect to the board surface on the basis of outputs from the load sensors, and there is a limit to the prevention of the mounting failure of the electronic component with an improvement in accuracy. Moreover, it is required to separately provide load sensors in a plurality of places of the apparatus in order to improve the measurement accuracy of the load, and it is difficult to detect the load in the neighborhood of the mounting position.

The present invention has been accomplished to solve the aforementioned conventional issues and has an object to provide an electronic component mounting apparatus capable of accurately detecting the mounting failure of the electronic component by detecting the load in the neighborhood of the mounting position.

Another object of the present invention is to solve the aforementioned conventional issues and provide an electronic component mounting apparatus capable of accurately measuring the load actually applied to the electronic component by eliminating the influence of an error due to sliding resistance when the movement block moves.

SUMMARY OF THE INVENTION

In accomplishing these and other aspects, according to a first aspect of the present invention, there is provided an electronic component mounting apparatus for mounting an electronic component on a board, the apparatus comprising:

-   -   a board holding section for holding the board;     -   a holding head for holding the electronic component;     -   a load sensor which is attached to the holding head or the board         holding section and has two piezoelectric elements for         generating voltages upon receiving horizontal loads in two         directions that are roughly perpendicular to a mounting         direction of the electronic component and roughly mutually         intersect each other, the piezoelectric elements being stacked         in the mounting direction; and     -   a mounting failure detection section for comparing a position in         a two-dimensional space in which horizontal load values in the         two directions detected by the load sensor are served as         coordinate values with a preset tolerance range in the         two-dimensional space and thus detecting mounting failure of the         electronic component.

According to a second aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the first aspect, further comprising:

-   -   a storage section for preparatorily storing a load profile that         expresses a time-base change in a load value in a direction         roughly parallel to the mounting direction to be applied to the         electronic component during mounting,     -   the load sensor further comprising a piezoelectric element for         generating a voltage upon receiving a vertical load in the         direction roughly parallel to the mounting direction, the         piezoelectric element being stacked on the two piezoelectric         elements, and     -   the mounting failure detection section detecting the mounting         failure of the electronic component by comparing a value of the         vertical load detected by the load sensor with the load profile         stored in the storage section.

According to a third aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the first or second aspect, wherein

-   -   the tolerance range in the two-dimensional space is expanded or         contracted around an origin of the two-dimensional space on         basis of the load profile.

According to a fourth aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the third aspect, wherein

-   -   the tolerance range in the two-dimensional space is a circular         or elliptic region centered around the origin.

According to a fifth aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the first or second aspect, wherein

-   -   a foreign object intruding between the electronic component and         the holding head or the board or between the board and the board         holding section during mounting is detected by the mounting         failure detection section.

According to a sixth aspect of the present invention, there is provided an electronic component mounting method for mounting an electronic component on a board, the method comprising of:

-   -   holding a board by means of a board holding section;     -   holding an electronic component by means of a holding head;     -   mounting the electronic component on the board;     -   detecting horizontal loads in two directions that are roughly         perpendicular to a mounting direction of the electronic         component and roughly mutually intersect each other by means of         a load sensor that has two piezoelectric elements attached to         the holding head or the board holding section in the mounting;         and     -   detecting mounting failure of the electronic component by         comparing a position in a two-dimensional space in which         horizontal load values in the two directions detected by the         load sensor are served as coordinate values with a preset         tolerance range in the two-dimensional space.

According to a seventh aspect of the present invention, there is provided an electronic component mounting apparatus for mounting an electronic component on a board, the apparatus comprising:

-   -   a movement block capable of being driven in a mounting direction         of the electronic component;     -   a holding head which is an integrated block of high rigidity for         holding the electronic component;     -   a load sensor which is provided between the movement block and         the holding head and supports the holding head, for detecting         vertical load value in a direction roughly parallel to the         mounting direction;     -   a guide mechanism for movably guiding the movement block in the         mounting direction; and     -   a drive mechanism for driving the movement block in the mounting         direction.

According to an eighth aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the seventh aspect, further comprising:

-   -   a storage section for preparatorily storing a load profile that         expresses a time-base change in a load value in a direction         roughly parallel to the mounting direction to be applied to the         electronic component during mounting;     -   a control section for controlling driving of the movement block         according to the load profile; and     -   a mounting failure detection section for detecting mounting         failure of the electronic component by comparing the vertical         load value in the direction roughly parallel to the mounting         direction detected by the load sensor with the load profile.

According to a ninth aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the eighth aspect, further comprising:

-   -   a displacement sensor for detecting a displacement amount in the         direction roughly parallel to the mounting direction of the         holding head, and     -   the mounting failure detection section detecting the mounting         failure of the electronic component by comparing the         displacement amount of the holding head from start to end of         mounting detected by the displacement sensor with a reference         displacement amount preparatorily stored in the storage section.

According to a 10th aspect of the present invention, there is provided the electronic component mounting apparatus as defined in any one of the seventh through ninth aspects, wherein

-   -   the load sensor is a piezoelectric element.

According to an 11th aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the 10th aspect, wherein

-   -   the load sensor has three piezoelectric elements for generating         voltages upon receiving a vertical load roughly parallel to the         mounting direction and horizontal loads in two directions that         are roughly perpendicular to the mounting direction and roughly         mutually intersect each other.

According to a 12th aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the 11th aspect, wherein

-   -   the mounting failure detection section detects the mounting         failure of the electronic component by comparing a position in a         two-dimensional space in which horizontal load values in the two         directions detected by the load sensor are served as coordinate         values with a tolerance range in the two-dimensional space         preparatorily stored in the storage section.

According to a 13th aspect of the present invention, there is provided the electronic component mounting apparatus as defined in the 10th aspect, wherein

-   -   the piezoelectric element is made of piezoelectric ceramics or         crystal.

According to a 14th aspect of the present invention, there is provided the electronic component mounting apparatus as defined in any one of the seventh through ninth aspects, wherein

-   -   the electronic component is a semiconductor bare chip.

According to a 15th aspect of the present invention, there is provided the electronic component mounting apparatus as defined in any one of the seventh through ninth aspects, wherein

-   -   the electronic component is bonded to the board via a         thermosetting resin by being heated with a prescribed load         applied thereto.

According to a 16th aspect of the present invention, there is provided the electronic component mounting apparatus as defined in any one of the seventh through ninth aspects, wherein

-   -   the electronic component is bonded to the board by ultrasonic         waves applied with a prescribed load applied thereto.

According to a 17th aspect of the present invention, there is provided the electronic component mounting apparatus as defined in any one of the seventh through ninth aspects, wherein

-   -   the load sensor comprises:     -   an attachment face to which the holding head is affixed; and     -   an another attachment face that is parallel to the attachment         face and attached to the movement block.

According to an 18th aspect of the present invention, there is provided an electronic component mounting method for mounting an electronic component on a board, the method comprising of:

-   -   holding a board by means of a board holding section;     -   holding the electronic component by a holding head that is an         integrated block of high rigidity attached to a movement block         driven in a mounting direction of the electronic component via a         load sensor;     -   mounting the electronic component on the board by driving the         movement block in the mounting direction along a guide         mechanism; and     -   detecting a vertical load in a direction roughly parallel to the         mounting direction by means of the load sensor simultaneously         with the mounting of the electronic component.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:

FIG. 1 a front view showing the construction of an electronic component mounting apparatus according to a first embodiment of the present invention;

FIG. 2 is a sectional view showing the installation structure of the holding head and the load sensor of the electronic component mounting apparatus of the first embodiment;

FIG. 3 is a chart showing the flow of the electronic component mounting operation of the electronic component mounting apparatus of the first embodiment;

FIG. 4 is a graph showing the load profile of the electronic component mounting apparatus of the first embodiment;

FIG. 5 is a chart showing the flow of operation for detecting the mounting failure of the electronic component of the electronic component mounting apparatus of the first embodiment;

FIG. 6 is a chart showing the tolerance range of a horizontal load applied to the electronic component of the electronic component mounting apparatus of the first embodiment;

FIG. 7 is a view showing the neighborhood of the electronic component of the electronic component mounting apparatus of the first embodiment;

FIG. 8 is a view showing the neighborhood of the electronic component of the electronic component mounting apparatus of the first embodiment;

FIG. 9 is a view showing the neighborhood of the electronic component of the electronic component mounting apparatus of the first embodiment;

FIG. 10 is a sectional view showing another example of the installation structure of the holding head and the load sensor of the electronic component mounting apparatus of the first embodiment;

FIG. 11 is a front view showing the construction of an electronic component mounting apparatus according to a second embodiment of the present invention; and

FIG. 12 is a front view showing the construction of a conventional electronic component mounting apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.

Embodiments of the present invention will be described in detail below on the basis of the drawings.

The present invention is related to an electronic component mounting apparatus capable of accurately detecting the mounting failure of an electronic component by detecting the load in the neighborhood of the mounting position and accurately measuring a load applied to the electronic component by eliminating the influence of the sliding resistance of a guide mechanism with a load sensor provided in the neighborhood of a holding head. An electronic component mounting apparatus according to one embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing the construction of the electronic component mounting apparatus 10 according to the first embodiment of the present invention, where the electronic component mounting apparatus 10 mounts an electronic component 1 that is a semiconductor bare chip on a board 2 on which circuit wiring is formed.

In the electronic component mounting apparatus 10, a nut section 21 provided in a movement block 20 that moves in the Z-direction is meshed with a feed screw 51 that is rotationally driven by a motor 50. A slider 11 is provided on a side surface of the movement block 20 and slides on a guide rail 12 directed in the Z-direction. The slider 11 and the guide rail 12 serve as a guide mechanism for movably guiding the movement block 20 in the mounting direction of the electronic component 1. Moreover, the motor 50, the feed screw 51 and the nut section 21 of the movement block 20 constitute a drive mechanism for driving the movement block 20 in the mounting direction of the electronic component 1.

At the lower end portion of the movement block 20 are provided a shaft 13 whose central axis is arranged in the Z-direction, a load sensor 30 that has a piezoelectric element for measuring the load applied to the electronic component 1, a block 141 to which a ultrasonic vibrator 14 is attached, and a holding section 15 for sucking and holding the electronic component 1 by a negative pressure, which are arranged in this order. The holding section 15, the block 141, and members provided between the holding section 15 and the block 141 are assembled as a holding head 15 a that is an integrated block of high rigidity. Piping 16 connected to a vacuum pump (not shown) is connected to the holding section 15, and the electronic component 1 is sucked by carrying out suction from a suction port formed on the lower surface of the holding section 15. An optical system (optical interference system) linear scale 70, which is a displacement sensor for detecting the displacement amount in the Z-direction of the holding head 15 a (mounting direction of the electronic component 1), is provided on the (+X) side of the shaft 13. Outputs of the linear scale 70 and the load sensor 30 are inputted to a control section 60.

A table 40, which can be moved in the X-direction and the Y-direction, is provided below the holding head 15 a, and the board 2 is placed and held on the table 40. It is to be noted that a mechanism for feeding the electronic component 1 and a camera for detecting the relative position of the electronic component 1 with respect to the board 2 and so on are not shown in the figures.

FIG. 2 shows the installation structure of the load sensor 30 and the holding head 15 a. The block 141 to which the ultrasonic vibrator 14 is attached and the load sensor 30 are provided with through holes 141 a and 30 a through which a bolt 35 penetrates, and the block 141 and the load sensor 30 are attached to the shaft 13 by means of the bolt 35 so that the load sensor 30 is interposed between the block 141 and the shaft 13 of the movement block 20. That is, the holding head 15 a is attached so as to be supported by substantially only the load sensor 30. Moreover, the holding section 15 is attached to the block 141 by means of a bolt (not shown).

In the load sensor 30, flat-plate-shaped three piezoelectric elements 31, 32 and 33 are stacked in layers in the Z-direction (mounting direction of the electronic component 1). For example, the direction of polarization of the piezoelectric element 31 located in the uppermost layer is determined so that a voltage is generated upon receiving a load (load in the direction perpendicular to the board 2, hereinafter referred to as a “vertical load”) in the direction roughly parallel to the mounting direction of the electronic component 1 (Z-direction shown in FIG. 1, and this is not necessarily required to coincide with the gravitational direction). Likewise, the directions of polarization of the piezoelectric elements 32 and 33 located in the intermediate layer and the lowermost layer are determined so that a voltage is generated upon receiving a load (hereinafter referred to as a “horizontal load”) in the two directions (X-direction and Y-direction) that are roughly perpendicular to the mounting direction of the electronic component 1 and roughly perpendicularly to each other.

The load sensor 30 has an attachment face 30 b to which the holding head 15 a is directly attached and another attachment face 30 c that is parallel to the attachment face 30 b and attached to the shaft 13 of the movement block 20. With this arrangement, it is achieved to attach to and detach the load sensor 30 and from the shaft 13 by means of one bolt 35 easily in a prescribed posture.

FIG. 3 is a chart showing the flow of the operation of the electronic component mounting apparatus 10 in mounting the electronic component 1 on the board 2. In mounting the electronic component 1 on the board 2, the board 2 is first placed and held on the table 40 (step S11), and the holding section 15 receives the electronic component 1 from a feed mechanism and holds the component by vacuum suction (step S12). Subsequently, the electronic component 1 moves to a place above the mounting position on the board 2, and alignment of the relative position of the electronic component 1 held by the holding section 15 with respect to the board 2 is carried out (step S13).

Next, the motor 50 is rotationally driven in a prescribed direction to move down the holding section 15 together with the movement block 20 in the (−Z)-direction (step S14), so that the electronic component 1 is brought in contact with the board 2. The contact of the electronic component 1 with the board 2 is accurately detected by a contact detection section 61 of the control section 60 shown in FIG. 1 on the basis of the output of the load sensor 30 (step S15). When the required accuracy of the detection of the contact of the electronic component 1 with the board 2 is not comparatively high, the contact may be detected by a relation between the displacement amount in the Z-direction (mounting direction) of the electronic component 1 detected by the linear scale 70 and a current supplied to the motor 50 (torque of the motor). Moreover, it is acceptable to detect the descent of the holding head 15 a by a prescribed distance according to an output from an encoder of the motor 50 and regard the detection as the contact of the electronic component 1 with the board 2.

FIG. 4 is a graph showing a load profile 601, representing a time-base change in the vertical load to be applied to the electronic component 1 at the time of the mounting, and the load profile 601 has preparatorily been stored in a storage section 62 of the control section 60. The load profile 601 shown in FIG. 4 represents the fact that the load gradually increases from the start of the mounting to a time t1, pressurization with a prescribed load is effected only for a prescribed time from the time t1, the load further increases to a time t2, and thereafter pressurization is effected for a prescribed time from the time t2. It is to be noted that the configuration of the load profile 601 is variously changed in accordance with the types of the electronic component 1 and the board 2, the mounting method, and so on.

When the contact of the electronic component 1 with the board 2 is detected in step S15, the driving of the movement block 20 is controlled by the control section 60 according to the load profile 601, and the pressurization of the electronic component 1 is started (step S16). Then, in a state in which the electronic component 1 is pressurized with a prescribed load as a consequence of a gradual increase in the load detected by the load sensor 30, the ultrasonic vibrator 14 is activated by a signal from the control section 60 to apply ultrasonic waves to the electronic component 1. Consequently, the bumps 1 a provided at the bottom of the electronic component 1 are bonded to the wiring pattern on the board 2, so that mounting is carried out concurrently with placement (step S17)

Subsequently, a valve (not shown) provided for the piping 16 is opened with blow effected from the holding section 15 via the piping 16, and the holding section 15 is separated from the electronic component 1. Then, the motor 50 is rotationally driven in the reverse direction to move up the movement block 20 (and the holding head 15 a) in the (+Z)-direction, completing the mounting of the electronic component 1 (step S18).

In the electronic component mounting apparatus 10, if some trouble occurs in the load applied to the electronic component 1 or the displacement of the electronic component 1 in mounting the electronic component 1 on the board 2 (steps S16 and S17), then the mounting failure (abnormality) of the electronic component 1 is detected by the control section 60 on the basis of outputs from the load sensor 30 and the linear scale 70. FIG. 5 is a chart showing the flow of operation for detecting the mounting failure of the electronic component 1 in the electronic component mounting apparatus 10. Hereinafter, the failure detection operation in mounting the electronic component 1 (e.g., failure detection operation carried out simultaneously with the mounting process of the electronic component 1) will be described below with reference to FIG. 5 and other figures.

First of all, if the contact of the electronic component 1 with the board 2 is detected and the pressurization of the electronic component 1 is started, then the load applied to the electronic component 1 is detected by the load sensor 30 and transferred to the control section 60 (step S21). The vertical load detected by the piezoelectric element 31 is compared with the load profile 601 stored in the storage section 62 to confirm whether or not the load is within the tolerance range (range between the lines 6021 located above and below the load profile 601) 602 of the load profile 601 shown in FIG. 4 (step S22). Moreover, simultaneously with the detection of contact of the electronic component 1 with the board 2, measurement of the displacement amount of the holding head 15 a by the linear scale 70 is also started.

If it is determined that the vertical load is outside the tolerance range 602 of the load profile 601 by a mounting failure detection section 63 (see FIG. 1) of the control section 60, the operator is informed of the detection of the mounting failure of the electronic component 1 by lighting a warning lamp 64 provided for the electronic component mounting apparatus 10 (step S30). For example, if sliding failure or the like of the slider 11 or the guide rail 12 occurs, then the detected vertical load sometimes has a small value outside the tolerance range 602 of the load profile 601. In this case, there is the possibility of the occurrence of defective bonding of the bumps 1 a to the board 2 due to a shortage of pressure of the electronic component 1 against the board 2, and such the mounting failure is detected by the mounting failure detection section 63.

If it is determined that the vertical load is within the tolerance range 602 of the load profile 601, then the horizontal load detected by the piezoelectric elements 32 and 33 are next compared with the tolerance range of the horizontal load preparatorily stored in the storage section 62. FIG. 6 is a chart showing a tolerance range 603 of the horizontal load applied to the electronic component 1 in a two-dimensional space 604 in which the X-direction and the Y-direction of the load are served as the X-axis and the Y-axis. The tolerance range 603 is a region of a circle or an ellipse (another shape may be sometimes adopted according to the configuration and so on of the electronic component 1) which is centered at the origin of the two-dimensional space 604 encircled by a line 6031, and the region is expanded or contracted around the origin located at the center on the basis of the load profile 601. In FIG. 6, the line 6031 indicated by the solid line indicates the tolerance range 603 at the time t1 of the load profile 601 shown in FIG. 4. If the pressurization of the electronic component 1 is promoted and the pressurization enters the state of the load profile 601 at the time t2, then the region is expanded to the position indicated by the two-dot chain line on the basis of the value or the like of the vertical load represented by the load profile 601 at the time t2.

In the mounting failure detection section 63 of the control section 60, a position, in which the horizontal load values in the X-direction and the Y-direction detected by the load sensor 30 are served as the coordinate values, is compared with the tolerance range 603 (step S23). When the position is outside the tolerance range 603, the operator is informed of the detection of the mounting failure of the electronic component 1 by lighting the warning lamp 64 (step S30). As the case of the mounting failure detected in step S23, it can be considered, for example, the case where the electronic component 1 is held inclined with respect to the board 2 due to suction failure of the holding section 15, intrusion of a foreign object or the like and the case where a foreign object intrudes between some bumps 1 a and the board 2.

FIGS. 7 through 9 are views showing the neighborhood of the electronic component 1 held by the holding section 15. As shown in FIGS. 7 through 9, when the intrusion of a foreign object 80 occurs on the (+X) side with respect to the center of the electronic component 1 between the electronic component 1 and the holding section 15 or the board 2 or between the board 2 and the table 40, a bump 1 a located on the (+X) side of the electronic component 1 is brought in contact with the board 2 (via the foreign object 80 in the case shown in FIG. 8) earlier than a bump 1 a located on the (−X) side, and the pressurization of the electronic component 1 is started from this state. At this time, due to the concentration of the load on the bump 1 a located on the (+X) side, the position in the two-dimensional space 604 of the horizontal load detected by the load sensor 30 deviates from the origin to the (+X) side and becomes located outside the tolerance range 603. In this case, the load is not uniformly applied to the bumps 1 a at the bottom of the electronic component 1, possibly causing the collapse of the bump 1 a located on the (+X) side due to the concentration of the load, defective bonding between the bump 1 a located on the (−X) side to the board 2 and further damage of the electronic component 1 itself due to the nonuniform pressurization. The mounting failure caused by such the deviation of the horizontal load is detected by the mounting failure detection section 63.

In the electronic component mounting apparatus 10, the position in the space 604 that expresses the horizontal load applied to the electronic component 1 due to the intrusion of the foreign object 80 or the like is outside the tolerance range 603 when the position deviates not only in the (+X) direction but also in another direction, and the mounting failure is detected by the mounting failure detection section 63.

If it is determined that the horizontal load is within the tolerance range 603 by the mounting failure detection section 63, then it is confirmed whether or not the mounting of the electronic component 1 is ended by the control section 60 (step S24). If the mounting is not ended, the program flow returns to step S21 to repeat the measurement of the load and the detection of the mounting failure (steps S21 through S23) until the mounting of the electronic component 1 (pressurization of the electronic component 1 carried out in accordance with the load profile 601) ends (step S24).

If the mounting of the electronic component 1 is ended, then the displacement amount of the holding head 15 a from the start of the mounting of the electronic component 1 (at the time of detection of the contact of the electronic component 1 with the board 2) to the end (end of the pressurization of the electronic component 1) is detected by the linear scale 70, transferred to the control section 60 (step S25) and compared with a displacement amount that becomes a reference (hereinafter referred to as a “reference displacement amount”) preparatorily stored in the storage section 62 (step S26).

If the detected displacement amount is outside the tolerance range preparatorily related to the reference displacement amount, then the operator is informed of the detection of the mounting failure of the electronic component 1 by lighting the warning lamp 64 by means of the mounting failure detection section 63, and the detection operation of the mounting failure ends (step S30). For example, if the electronic component 1 comes close to the board 2 more than necessary as a consequence of the collapse of the bump 1 a of the electronic component 1 at the time of mounting or for another reason, then the detected displacement amount takes a great value outside the tolerance range, and such the mounting failure is detected by the mounting failure detection section 63.

Moreover, if the displacement amount detected by the linear scale 70 is within the tolerance range of the reference displacement amount, then it is determined that the placement (and mounting) of the electronic component 1 on the board 2 has been normally ended, and the detection operation of the mounting failure ends. As described above, in the electronic component mounting apparatus 10, by comparing the detection results of the load sensor 30 and the linear scale 70 with the tolerance range preparatorily stored in the storage section 62, the mounting failure of the electronic component 1 is detected by the mounting failure detection section 63. In the electronic component mounting apparatus 10, the mounting operation of the electronic component 1 is continued when the degree of the mounting failure is negligible even if the mounting failure is detected in steps S22 and S23, and the detection of the load and the displacement by the load sensor 30 and the linear scale 70 is continued until the mounting operation sequence ends, consequently obtaining the measurement results in the steps (steps S22, S23 and S26) for detecting the mounting failure.

FIG. 10 is a view showing another example of the installation structure of the load sensor 30 and the holding head 15 a. In FIG. 10, a heat block 142 having a heater is attached in place of the block 141, and a semiconductor bare chip, which is an IC as the electronic component 1, is held by the holding section 15, as compared with the structure shown in FIG. 2. The holding head 15 a is assembled as an integrated block of high rigidity with the holding section 15 and the heat block 142. The other constructions are similar to those of FIG. 2, and they are denoted by same reference numerals. The structure and the installation method of the load sensor 30 are also similar to those of FIG. 2. The load sensor 30 and the heat block 142 can be easily attached to or detached from the shaft 13 by means of a bolt 35. Moreover, a linear scale 70 for measuring the displacement in the Z-direction of the holding head 15 a is provided on the (+X) side of the shaft 13.

In mounting the electronic component 1, a thermosetting anisotropic conductive resin film (ACF (Anisotropic Conductive Film)) (hereinafter referred to as an “ACF”) 2 a is preparatorily stuck on the board 2, and the holding section 15 is preheated by the heat block 142. Therefore, when the electronic component 1 is held by the holding section 15, the electronic component 1 is heated via the holding section 15. Then, the holding section 15 is moved down to pressurize the electronic components 1 on the board 2 via the ACF 2 a, and the conductive particles in the ACF 2 a are collapsed to electrically bond the electrodes 1 b of the electronic component 1 to the electrodes on the board 2. Concurrently with the bonding, the ACF 2 a is heated and hardened via the electronic component 1, so that the electronic component 1 is fixed on the board 2. After the bonding ends, the holding section 15 releases suction and moves up.

Materials suitable for the piezoelectric element for the load sensor 30 will be described next. Table 1 shows relations between the materials of the piezoelectric element and various constants. TABLE 1 CONSTANTS OF PIEZOELECTRIC ELEMENTS Curie Piezoelectric Piezoelectric Point Dielectric Distortion Output Temperature (Tc) Constant Constant (d) Coefficient (g) Coefficient ° C. ε/ε₀ m/v × 10⁻¹² Vm/N × 10⁻⁸ d (%/° C.) g (%/° C.) Lead 320.0 2,000.0 320.0 24.0 +0.08 −0.19 Zirconate Titanate Pb(Ti, Zr) O₃ Lead 490.0 300.0 50.0 30.0 +0.15 +0.04 Titanate PbTiO₃ Crystal 550.0 4.5 2.0 50.0 −0.02 −0.02 Lead 560.0 250.0 82.0 30.0 +0.06 +0.02 Niobate PbNb₂O₆ Lithium 1,210.0 30.0 16.0 2.3 +0.03 — Niobate LiNbO₃

For example, the crystal, of which dielectric constant and piezoelectric distortion constant are low and the sensitivity is low, has high Curie point and excellent stability. Therefore, when the bonding is carried out by means of a heater as shown in FIG. 10 and a measurement accuracy is required, it is preferable to use crystal. On the other hand, the piezoelectric ceramics such as lead zirconate titanate (Pb(TiZr)O₃), of which the Curie point is lower than of crystal, has high dielectric constant and high piezoelectric distortion constant and an excellent response characteristic. Moreover, the piezoelectric ceramics have a feature that they are easy to process into an arbitrary configuration and excellent in mass productivity. For the above reasons, an optimum one is selected from the group consisting of crystal and piezoelectric ceramics in accordance with the accuracy, response characteristic, cost and so on required for the load sensor 30.

As described above, in the electronic component mounting apparatus 10, by detecting the horizontal load utilizing the piezoelectric elements 32 and 33 provided in a stack in the mounting direction of the electronic component 1 and detecting the vertical load utilizing the piezoelectric element 31 provided superposed on the piezoelectric elements 32 and 33, it is possible to reduce the size in the horizontal direction of the load sensor 30 and detect the load applied in the three directions to the electronic component 1 at the neighborhood of the mounting position of the electronic component 1. As a result, it is possible to more accurately measure the load applied to the electronic component 1.

Moreover, the load sensor 30 is directly attached to the holding head 15 a that is the integrated block of high rigidity, and therefore, the load value detected by the load sensor 30 can be regarded as equivalent to the load applied to the electronic component 1. In particular, the load sensor 30 is arranged on the holding head 15 a side with respect to the sliding portion of the slider 11 and the guide rail 12 in the Z-direction that is the mounting direction of the electronic component 1, and therefore, the load value detected by the load sensor 30 does not receive the influence of the sliding resistance between the slider 11 and the guide rail 12. Therefore, in comparison with the conventional electronic component mounting apparatus, a measurement value close to the real load actually applied to the electronic component 1 can be obtained, and the load applied to the electronic component 1 in mounting the electronic component 1 can be more accurately measured.

In the electronic component mounting apparatus 10, by comparing the vertical load applied to the electronic component 1 with the load profile 601 and detecting the deviation of the horizontal load applied to the electronic component 1 and/or the abnormality in the displacement amount of the electronic component 1 at the time of mounting, the mounting failure at the time of mounting the electronic component 1 can be accurately detected. Then, by removing the board 2 of which the mounting failure is detected as a defective component from the mass production process, the occurrence of defective electronic equipment as a finished product can be prevented in advance.

In the electronic component mounting apparatus 10, it is acceptable to execute by the control section 60 feedback control of the motor 50 that pressurizes the electronic component 1 against the board 2 by driving the holding head 15 a on the basis of the result of comparison between the measurement value of the vertical load detected by the load sensor 30 and the load profile 601. As described above, in the electronic component mounting apparatus 10, the vertical load applied to the electronic component 1 can be accurately measured. Therefore, accurate control of the motor 50 can be executed, and it becomes possible to make variations in the vertical load applied to the electronic component 1 fall within a range of several grams. As a result, the defective bonding of the electronic component 1 to the board 2, the damage of the bumps 1 a and the electrodes 1 b at the bottom of the electronic component 1, the damage of the electronic component 1 itself, or the like can be prevented from occurring.

In the electronic component mounting apparatus 10, the position, in which the horizontal load values in the X-direction and the Y-direction are served as the coordinate values in the two-dimensional space 604, is compared with the tolerance range 603 that is a circular or elliptic region centered around the origin of the two-dimensional space 604. That is, the tolerance range 603 is determined with respect to the synthetic vector of the weight vectors in the X-direction and the Y-direction, and therefore, the detection of the mounting failure can be carried out by taking the deviations of the load in the X-direction and the Y-direction comprehensively into account. Moreover, by virtue of the elliptic tolerance range 603, the major axis and the minor axis of the ellipse can be changed in correspondence with the configuration of the electronic component 1, a difference in sensitivity between the piezoelectric element 32 in the X-direction and the piezoelectric element 33 in the Y-direction, or the like, and the tolerance range 603 can be appropriately set.

The load sensor, which employs the piezoelectric element, has a wider measurable range of the load than that of the load cell that employs a strain gauge. Moreover, both the crystal and piezoelectric ceramics, which are the materials of the piezoelectric element, have almost no hysteresis of elastic deformation since they have higher rigidity and a smaller amount of deformation than the metallic elastic body that constitutes the load cell. Therefore, the load applied to the electronic component 1 can be more accurately measured. Furthermore, the load sensor, which employs the piezoelectric element, has a high response speed than when a load cell is employed. Therefore, the contact of the electronic component 1 with the board 2 can be more accurately detected, and the load applied to the electronic component 1 can be accurately measured even when the electronic component is mounted at high speed. Therefore, by employing the piezoelectric elements 31 through 33 for the load sensor 30, an electronic component mounting apparatus 10 of higher versatility can be provided.

FIG. 11 is a view showing an electronic component mounting apparatus 10 a according to the second embodiment of the present invention. In the electronic component mounting apparatus 10 a, based on the electronic component mounting apparatus 10 shown in FIG. 1, the load sensor 30 provided between the block 141 and the shaft 13 of the movement block 20 is provided under the table 40 (on the (−Z)-side), and the table 40 is supported on a base 41 via the load sensor 30. The other constructions are similar to those of FIG. 1, and they are denoted by same reference numerals in the following description.

In the electronic component mounting apparatus 10 a, when the electronic component 1 held by the holding section 15 is mounted on the board 2 while being pressurized, the load applied to the board 2 (i.e., the load applied to the electronic component 1) is measured by the load sensor 30 arranged vertically below the holding section 15.

The mounting operation of the electronic component 1 by the electronic component mounting apparatus 10 a is similar to that of the first embodiment. First of all, the board 2 is placed and held on the table 40, and the electronic component 1 sucked and held by the holding section 15 is moved down to the mounting position on the board 2, and the contact of the electronic component 1 with the board 2 is detected by the contact detection section 61 of the control section 60. Subsequently, the pressurization of the electronic component 1 is started in accordance with the load profile 601 (see FIG. 4) preparatorily stored in the storage section 62, and the placement and mounting of the electronic component 1 are concurrently carried out by ultrasonic waves applied to the electronic component 1 pressurized with a prescribed load. Thereafter, the holding head 15 a is moved up to complete the mounting of the electronic component 1 (FIG. 3: steps S11 through S18).

Even in the electronic component mounting apparatus 10 a, the mounting failure of the electronic component 1 is detected by the mounting failure detection section 63 on the basis of the outputs from load sensor 30 and the linear scale 70 at the time of mounting the electronic component 1. The detection operation of the mounting failure is also similar to that of the first embodiment. First of all, the vertical load and the horizontal load are detected by the piezoelectric elements 31 through 33 of the load sensor 30 (FIG. 5: step S21), and it is confirmed whether or not the vertical load is within the tolerance range 602 of the load profile 601 (step S22). If the vertical load is outside the tolerance range 602, then the mounting failure of the electronic component 1 is detected, and the warning lamp 64 is lit (step S30).

If the vertical load is within the tolerance range 602, then the position, in which the horizontal load values in the X-direction and the Y-direction are served as the coordinate values in the two-dimensional space 604 in which the X-direction and the Y-direction of the load are served as the X-axis and the Y-axis, is compared with the tolerance range 603 of the horizontal load (step S23). If the position is outside the tolerance range 603, the mounting failure of the electronic component 1 is detected (step S30). In the electronic component mounting apparatus 10 a, the detection of the mounting failure is repeated until the mounting of the electronic component 1 ends (step S24).

If the mounting of the electronic component 1 ends, then the displacement amount in the Z-direction of the holding head 15 a from the start to the end of the mounting of the electronic component 1 is detected by the linear scale 70 and compared with the reference displacement amount (steps S25 and S26). The mounting failure of the electronic component 1 is detected when the displacement amount falls outside the tolerance range of the reference displacement amount (step S30), and the detection operation of the mounting failure ends when the displacement amount falls within the tolerance range.

As described above, the electronic component mounting apparatus 10 a is able to detect the load applied to the electronic component 1 at the neighborhood of the mounting position of the electronic component 1 while reducing the size in the horizontal direction of the load sensor 30 by means of the piezoelectric elements 31 through 33 provided in a stack in the mounting direction of the electronic component 1 similarly to the first embodiment. Moreover, the load sensor 30 is provided just under the mounting position of the electronic component 1 in the position in which the influence of the sliding resistance of the slider 11 and the guide rail 12 is not exerted, and therefore, the load applied to the electronic component 1 can be more accurately measured.

In the electronic component mounting apparatus 10 a, by comparing the vertical load applied to the electronic component 1 with the load profile 601 or detecting the deviation of the horizontal load applied to the electronic component 1 and the abnormality in the displacement amount of the electronic component 1 at the time of mounting, the mounting failure at the time of mounting the electronic component 1 can be accurately detected. Furthermore, by comparing the deviation of the horizontal load with the tolerance range 603 appropriately set in correspondence with the configuration of the electronic component 1 and so on, the detection of the mounting failure can be carried out taking the deviations in the X-direction and the Y-direction comprehensively into account.

Moreover, by employing the piezoelectric elements 31 through 33 for the load sensor 30, the electronic component mounting apparatus 10 a of higher versatility can be provided.

Although the embodiments of the present invention have been described above, the present invention is not limited to the aforementioned embodiments but allowed to be modified in a variety of ways.

For example, a ball spline may be employed as a mechanism for guiding the movement of the movement block 20. In this case, the direction of the electronic component may be made changeable by pivoting the entire ball spline around the central axis.

Moreover, although the piezoelectric element has been employed as the load sensor in the aforementioned embodiments, a load cell may be employed similarly to the conventional case depending on the magnitude of the load and the load detection accuracy. Even in the above case, a measurement value close to the real load actually applied to the electronic component can be obtained since no error component ascribed to the sliding resistance of the guide mechanism or the like is included in the load detected by the load sensor, and the load to be applied to the electronic component at the time of mounting the electronic component can be more accurately controlled.

The electronic component mounting apparatus can be utilized for various cases of mounting various electronic components. For example, it is acceptable to preparatorily mount (temporary bond) an electronic component to, for example, solder bumps on a board by means of the electronic component mounting apparatus and bond the electronic component to the board by melting and solidifying the solder by reflow in the next process. Moreover, it is acceptable to temporarily pressure-bond an electronic component onto a board on which a thermosetting resin film has been stuck and use the electronic component mounting apparatus for the main pressure bonding to be carried out separately with pressurization and heating.

The electronic component to be mounted by the electronic component mounting apparatus may be, for example, an electronic component other than a semiconductor light-emitting element of an LED chip, a semiconductor laser, or the like, a packaged IC, a fine semiconductor chip of a resistor, a capacitor, or the like, or an SAW (Surface Acoustic Wave) filter other than semiconductor. The board may be formed of a material of glass, semiconductor, or the like other than resin. The electronic component may be held in the mounting stage by a mechanical chuck or an electrostatic chuck besides the suction with a negative pressure of the aforementioned embodiments.

The present invention can be utilized for the electronic component mounting apparatus that mounts an electronic component on a circuit board.

According to the present invention, by detecting the horizontal load by means of the piezoelectric elements, the size in the horizontal direction of the load sensor can be reduced, and the load can be detected at the neighborhood of the mounting position. Moreover, the mounting failure of the electronic component can be accurately detected from the deviation of the horizontal load. According to the second aspect of the present invention, the mounting failure of the electronic component can be accurately detected from the vertical load.

According to the third aspect of the present invention, the tolerance range corresponding to the load profile can be set for the horizontal load. According to the fourth aspect of the present invention, the mounting failure can be detected by taking the deviations of the load in the X-direction and the Y-direction comprehensively into account.

According to the present invention, the load applied to the electronic component is measured by the load sensor provided between the movement block and the holding head. Therefore, the load applied to the electronic component at the time of mounting the electronic component can be more accurately measured without receiving the influence of the sliding resistance or the like due to the guide mechanism for guiding the movement block. According to the 10th aspect of the present invention, the load applied to the electronic component can be more accurately measured.

According to the eighth aspect of the present invention, the mounting failure of the electronic component can be accurately detected from the vertical load. According to the ninth aspect of the present invention, the mounting failure of the electronic component can be accurately detected from the deviation of the horizontal load. According to the 12th aspect of the present invention, the mounting failure of the electronic component can be accurately detected from the displacement amount of the electronic component.

According to the 17th aspect of the present invention, the load sensor can easily be attached and detached in a prescribed posture.

By properly combining the arbitrary embodiments of the aforementioned various embodiments, the effects possessed by the embodiments can be produced.

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom. 

1. An electronic component mounting apparatus for mounting an electronic component on a board, the apparatus comprising: a board holding section for holding the board; a holding head for holding the electronic component; a load sensor which is attached to the holding head or the board holding section and has two piezoelectric elements for generating voltages upon receiving horizontal loads in two directions that are roughly perpendicular to a mounting direction of the electronic component and roughly mutually intersect each other, the piezoelectric elements being stacked in the mounting direction; and a mounting failure detection section for comparing a position in a two-dimensional space in which horizontal load values in the two directions detected by the load sensor are served as coordinate values with a preset tolerance range in the two-dimensional space and thus detecting mounting failure of the electronic component.
 2. The electronic component mounting apparatus as claimed in claim 1, further comprising: a storage section for preparatorily storing a load profile that expresses a time-base change in a load value in a direction roughly parallel to the mounting direction to be applied to the electronic component during mounting, the load sensor further comprising a piezoelectric element for generating a voltage upon receiving a vertical load in the direction roughly parallel to the mounting direction, the piezoelectric element being stacked on the two piezoelectric elements, and the mounting failure detection section detecting the mounting failure of the electronic component by comparing a value of the vertical load detected by the load sensor with the load profile stored in the storage section.
 3. The electronic component mounting apparatus as claimed in claim 1, wherein the tolerance range in the two-dimensional space is expanded or contracted around an origin of the two-dimensional space on basis of the load profile.
 4. The electronic component mounting apparatus as claimed in claim 3, wherein the tolerance range in the two-dimensional space is a circular or elliptic region centered around the origin.
 5. The electronic component mounting apparatus as claimed in claim 1, wherein a foreign object intruding between the electronic component and the holding head or the board or between the board and the board holding section during mounting is detected by the mounting failure detection section.
 6. An electronic component mounting method for mounting an electronic component on a board, the method comprising of: holding a board by means of a board holding section; holding an electronic component by means of a holding head; mounting the electronic component on the board; detecting horizontal loads in two directions that are roughly perpendicular to a mounting direction of the electronic component and roughly mutually intersect each other by means of a load sensor that has two piezoelectric elements attached to the holding head or the board holding section in the mounting; and detecting mounting failure of the electronic component by comparing a position in a two-dimensional space in which horizontal load values in the two directions detected by the load sensor are served as coordinate values with a preset tolerance range in the two-dimensional space.
 7. An electronic component mounting apparatus for mounting an electronic component on a board, the apparatus comprising: a movement block capable of being driven in a mounting direction of the electronic component; a holding head which is an integrated block of high rigidity for holding the electronic component; a load sensor which is provided between the movement block and the holding head and supports the holding head, for detecting vertical load value in a direction roughly parallel to the mounting direction; a guide mechanism for movably guiding the movement block in the mounting direction; and a drive mechanism for driving the movement block in the mounting direction.
 8. The electronic component mounting apparatus as claimed in claim 7, further comprising: a storage section for preparatorily storing a load profile that expresses a time-base change in a load value in a direction roughly parallel to the mounting direction to be applied to the electronic component during mounting; a control section for controlling driving of the movement block according to the load profile; and a mounting failure detection section for detecting mounting failure of the electronic component by comparing the vertical load value in the direction roughly parallel to the mounting direction detected by the load sensor with the load profile.
 9. The electronic component mounting apparatus as claimed in claim 8, further comprising: a displacement sensor for detecting a displacement amount in the direction roughly parallel to the mounting direction of the holding head, and the mounting failure detection section detecting the mounting failure of the electronic component by comparing the displacement amount of the holding head from start to end of mounting detected by the displacement sensor with a reference displacement amount preparatorily stored in the storage section.
 10. The electronic component mounting apparatus as claimed in claim 7, wherein the load sensor is a piezoelectric element.
 11. The electronic component mounting apparatus as claimed in claim 10, wherein the load sensor has three piezoelectric elements for generating voltages upon receiving a vertical load roughly parallel to the mounting direction and horizontal loads in two directions that are roughly perpendicular to the mounting direction and roughly mutually intersect each other.
 12. The electronic component mounting apparatus as claimed in claim 11, wherein the mounting failure detection section detects the mounting failure of the electronic component by comparing a position in a two-dimensional space in which horizontal load values in the two directions detected by the load sensor are served as coordinate values with a tolerance range in the two-dimensional space preparatorily stored in the storage section.
 13. The electronic component mounting apparatus as claimed in claim 10, wherein the piezoelectric element is made of piezoelectric ceramics or crystal.
 14. The electronic component mounting apparatus as claimed in claim 7, wherein the electronic component is a semiconductor bare chip.
 15. The electronic component mounting apparatus as claimed in claim 7, wherein the electronic component is bonded to the board via a thermosetting resin by being heated with a prescribed load applied thereto.
 16. The electronic component mounting apparatus as claimed in claim 7, wherein the electronic component is bonded to the board by ultrasonic waves applied with a prescribed load applied thereto.
 17. The electronic component mounting apparatus as claimed in claim 7, wherein the load sensor comprises: an attachment face to which the holding head is affixed; and an another attachment face that is parallel to the attachment face and attached to the movement block.
 18. An electronic component mounting method for mounting an electronic component on a board, the method comprising of: holding a board by means of a board holding section; holding the electronic component by a holding head that is an integrated block of high rigidity attached to a movement block driven in a mounting direction of the electronic component via a load sensor; mounting the electronic component on the board by driving the movement block in the mounting direction along a guide mechanism; and detecting a vertical load in a direction roughly parallel to the mounting direction by means of the load sensor simultaneously with the mounting of the electronic component. 